What if the dark magic that 'infected' Luna was received by Celestia instead? All of a sudden, Twilight's freakouts in Swarm of the Century and Lesson Zero seem fully justified. For more evil Celestia, listen to Scarlett Peace's song The Other Side of the Sun.

This is the second image in my "thought experiment" series of images.

I'd always planned to do a Nightmare Moon version of Celestia at some stage; I just kept forgetting about it. Thanks to Skylark-Torch for feedback and for informing me that daymare is actually a real word; one that apparently means "a nightmarish fantasy experienced while awake"* and that its first known use was 1737. [Source]